The field of the present invention is refrigeration.
Commercial refrigeration has long employed absorption (Rankin cycle) or compression systems. Both of these systems require working process gas with specific thermodynamic characteristics. Chloro-fluorocarbon fluids, typically freon based, were used for many years. However, recent evidence suggests that these materials cause significant damage to the ozone layer around the Earth. New refrigerants are being developed in the hope of arresting if not reversing the damage.
Inefficient energy usage has also become of concern. Dwindling resources, increased population, energy costs, including the social costs of pollution, and the like have dictated more efficient energy uses. Refrigeration systems for air conditioning and other uses are understood to account for significant energy usage. Thus, efficient refrigeration systems are of significant importance.
Rotating machinery known to be used in refrigeration systems include compressors and turboexpanders. Rotary compressors are typically driven by motors through a shaft which may include gearing.
Turboexpanders typically include a radial inflow turbine rotor mounted within a housing having a radial inlet and an axial outlet. The turbine rotor is rotatably mounted within bearings through a shaft fixed to the rotor. Such turboexpanders may be used with a wide variety of different gas streams for such things as air separation, natural gas processing and transmission, recovery of pressure letdown energy from an expansion process, or thermal energy recovery from the waste heat of associated processes.
Three primary types of bearings that may be used to support the rotor shaft in turbo machinery are magnetic bearings, oil film bearings and gas bearings. Magnetic bearings provide superior performance over the other two bearings under many circumstances. Magnetic bearings have low drag losses, controlled stiffness and damping, and moderate load capacity. In addition, unlike oil film bearings, magnetic bearings do not require lubrication, thus eliminating oil, lines and associated components such as valves, pumps, filters, coolers and the like with the risk of process contamination.